1. The intro
2. The complexity of the characters
Every character has an intricate personality with different aspects, no matter if they have a major role or not. There is not someone who is purely good or purely evil and this is the most interesting!
3. The unpredictability
The fact that you don't know what is coming next is one of the key strenghts of the series. You don't know what's in store for your favourite characters (major or minor), you don't know how it'll end. And even though it hurts, Game of Thrones wouldn't be the same without this unpredictability.
4. The dynamic role of women
When in other fantasy series women are often sidelined, in Game of Thrones women play a major role. Badass ladies pull the strings, fight and make plans!
5. The diversity of the characters
Game of Thrones depicts among others, characters with physical and mental problems and how they manage to surpass them or not. This diversity makes the characters even more interesting.
6. The wide range of storylines
Even if certain characters or storylines bore you, you will definitely have others that excite you or speak to you.
7. The epic battles
8. The different houses
... And trying to find in which one you belong. The sigils, the words, the mentality, they're all an inseparable part of Game of Thrones.
9. The quotes
10. The realistic (as much as it can be) world
11. The connection with history
12. The mythical creatures
Fire-breathing dragons, giants, the Children of the Forest (even if they are now all dead), the frozen threat of the White Walkers...And since they do not actually exist (unfortunately) our dearest, poor direwolves must be included here!
13. The magic and time-travelling aspects
Here, I'm referring mostly to Bran. His warging and time-travelling capabilities are so exciting (and a bit confusing at the same time), especially in the last episodes. Waiting for more!
14. The religions
It is very interesting to get to know the religions of a fantasy world. It is even more interesting to have a variety of them, with different characteristics and values: The Faith of the Seven, the Old Gods, R'hllor, the Drowned God etc.
15. The beautiful places
16. The costumes and the hairstyles
The costumes of Game of Thrones are much more than what reaches the eye. They are products of great work, whether they look simple or not. We often don't get to see all the details. These costumes are purely works of art! Of course, it goes without saying that the same applies to all these intricate hairstyles as well!